@64173279 at least if you were to start a new game, Penny is always there. She's a part of every game with City Living until circumstances remove her. So as @BylineBelife is absolutely right and the chance may be lost to get the little Simlet back, if those steps don't return him you could start a new game and save Penny to your library. Then in your current game you can add her back and play the family again and just go back a few steps. You can recreate the child in CAS or just replay the family.
I can't remember if Penny is already in the library but you could check first. Or there may be a version of her in the gallery. But recreating the same circumstances is always possible when Sims are lost.
I've lost my entire game a few times due to bugs, in fact I lost all of my Sims in January so I'm in the process of recreating all of my Sims right now. I've done about 80 and have about 100 to go.
It also helps to run a backup game save incase Sims are lost in the game.
